In the encapsulating of electronic components mounted on a carrier, and more particularly in the encapsulating of semiconductor circuits (chips), use is generally made according to the prior art of encapsulating presses provided with two mould parts, into at least one of which are recessed mould cavities. After placing the carrier with the electronic components for encapsulating between the mould parts, the mould parts are moved toward each other such that they clamp the carrier. Encapsulating material is then supplied to the mould cavities and, after at least partial curing of the encapsulating material, the carrier with encapsulated electronic components is taken out of the encapsulating press. To limit the processing cycle of an encapsulating press it is desirable to move the mould parts toward each other rapidly and to reduce the speed only shortly before engaging on the products for encapsulating. A press is thus obtained which operates quickly but is also provided with soft close and therefore reduces the risk of damage to the products for processing. For this purpose various constructions have been developed in the past, such as for instance EP 0 935 520 in the name of the present applicant. Although a drive as described in this European patent provides the desired functionality it has the drawback that the drive is voluminous and heavy. This leads to a relatively expensive press which also takes up a considerable amount of space during use.
EP 1 284 179 discloses an apparatus for enhancing the closing force of an injection mould, more specifically for the production of shoes and soles. The mould is provided of two opposite mould parts displaceable relative to each other, feed means for moulding material and a drive mechanism for relative displacement of the mould parts. The drive mechanism consists of a cylinder with a first cylinder space fed by a feed line and a second cylinder space. By the movement of a piston in the second cylinder space a protruding part of a cylinder rod that is connected with the piston can be moved into the feed line of the first cylinder space to close the feed line off. This further movement of the protruding part of the cylinder rod pushes away the fluid in the first cylinder space. Due to the design of the double cylinder this results in enhancement of the closing force of the mould.
Object of the present invention is to provide a press of the type mentioned in the preamble which can be embodied in simpler, compact and light manner while it can still be closed at different speeds in a secure manner.
To this end the invention provides a press for encapsulating electronic components with encapsulating material according claim 1. A fluid bed is understood to mean a piston-like construction; a container open on one side and filled with a fluid which is covered by a replaceable wall part. Such a device has the advantage that for the rapid mutual displacement of the mould parts (the so-called “high speed movement”) an effective fluid drive requiring relatively little pressure can be used. Such a drive can take a very compact form and components are commercially available as inexpensive standard trade items. Another advantage of a fluid bed is that it can be assembled very compactly with a displaceable mould part. The displaceable mould part can connect directly onto the fluid bed, but in practice it is desirable for the exchangeability of mould parts that the fluid bed is covered by a displaceable wall part adapted for releasable coupling of a mould part. The drawback of a normal drive making use of a fluid bed for the high speed movement is however that it cannot be combined in a simple and reliable manner with a separate drive facility for the (slower) closing movement of the mould parts which moreover usually requires a greater pressure to be able to provide the desired closing pressure. The present invention now enables combining the advantages of the use of a fluid bed with the advantages of a press that can be operated at different speeds for different parts of the path of movement and has a drive which provides the required higher pressure only where this is necessary (when actually closing the press). Use is herein made of a displacer operable independently of the first fluid feed. In addition to the desired functionality of a different transmission ratio to facilitate the soft close of the mould parts with greater pressure the displacer also guarantees in inventive manner that when the displacer is activated the action of the high speed movement (first fluid feed to the fluid bed) is forcibly blocked. This means that the press has a forced process protection. The displacer is embodied such that it is operable by a cylinder onto which a second fluid feed connects such that the fluid bed and the cylinder are fed by a common fluid feed. This implies that the first fluid feed and second fluid feed are combined in a single and thus common fluid feed providing a very simple and efficient construction that is not only simpler to produce but also limits the chances for defects and limits the maintenance demands in relation to the closest prior art.
In a preferred embodiment variant the press also comprises a frame, which frame is provided with at least two plate-like frame parts placed substantially vertically adjacent to the displaceable mould parts. Such a construction of the press with plate-like frame parts situated on opposite sides of the mould parts, also designated as “plate press”, increases the possibilities for a compact construction of the press still further. Furthermore, the press can thus be manufactured in a relatively light and yet very stable manner. Another advantage is that a press with plate-like frame parts can be manufactured simply and thus relatively inexpensively.
In yet another embodiment variant the press is provided with a plurality of mutually adjacent displaceable mould parts, wherein for instance a separate fluid bed connects onto each of the mutually adjacent displaceable mould parts. By means of such a multiple press several products can be processed simultaneously (multi-strip) allowing for the press to compensate possible differences in height between the products for simultaneous processing. The capacity of the press can also be expanded in this manner without very heavy and large drive means being required. This again contributes to the possibility to embody the press compactly (even when it has a greater processing capacity).
It is desirable that the transmission ratio of the first fluid feed to the fluid bed is smaller than the transmission ratio of the cylinder to the fluid bed. In this manner the desired higher pressure level when closing the press can be easily achieved. The cylinder can be embodied as desired and depending on the circumstances as a pneumatic cylinder (air cylinder) or a hydraulic cylinder. When processing sensitive products such as semiconductors a pneumatic drive is generally preferred because this reduces the risk of contamination of the products.
In a specific embodiment variant the fluid bed is filled with solid particles. Alternatively it is of course also possible to fill the fluid bed with a liquid (such as for instance a liquid which is used in hydraulic systems). The advantage of solid particles is that the risk of leakage and therefore contaminations of the fluid bed is reduced.
In yet another embodiment variant the displaceable mould part forms part of the fluid bed. This means that the displaceable mould part also forms the displaceable part (the piston) of the fluid bed or is at least integrally formed with the displaceable cylinder part of the fluid bed. The displacer can likewise be embodied movable parallel to the contact surface of the displaceable mould part.
The displacer is preferably movable on the side of the displaceable mould part remote from the contact side and can furthermore be embodied such that it is displaceable parallel to the contact surfaces. This means that the displacer directly compresses the fluid bed. The pressure exerted by the displacer will thus be transmitted uniformly to the displaceable mould part. The construction height of the press can thus be kept particularly limited. The displacer can be embodied such that it can be forced completely into the fluid bed such that it is then situated under the displaceable mould part. The cylinder can also be situated under the displaceable mould part bat it is easier to allow it to protrude from the rear side (or front) of the press, since this space is available under normal operating conditions and in this manner the components of the press remain very easily accessible, for instance for check-up and maintenance.
The invention also provides a press for encapsulating electronic components with encapsulating material, comprising: two opposite mould parts displaceable relative to each other, feed means for encapsulating material, and a drive mechanism connecting onto at least one of the mould parts for mutual displacement of the mould parts, with the feature that at least one of the mould parts is provided with a displacer whereby the encapsulating material fed between the mould parts by the feed means can be placed under an increased pressure. Such a press also has the advantage that a feed of encapsulating material at relatively low filling pressure can be combined with a separately acting mechanism supplying the actual final filling pressure. The displacer can be embodied very compactly since placing a liquid encapsulating material under final filling pressure only requires very little compression. The displacer can thus be easily integrated in one of the mould parts.
In a preferred embodiment the displacer is formed by a displaceable pin integrated in a mould part and the displacer further preferably connects onto drive means for displacing the displacer. Such a displacer can be realized in a structurally very simple manner and at relatively very limited costs.
The displacer can moreover be embodied such that it is also adapted for releasing an encapsulated electronic component from the mould. Such a displacer is thereby directly provided with the functionality of a pusher pin or ejector pin. Reversely a known ejector pin (including the drive of such an ejector pin) can also be employed as displacer according to the present invention provided the actuation of the drive is adapted for this purpose. The drive mechanism of one or more ejector pins can thus also be used as drive of one or more displacers.
In yet a further embodiment variant it is possible that the displacer connects onto a passage for encapsulating material arranged in the mould parts. It is of course necessary that the displacer engages directly on (respectively acts on) the fed encapsulating material. When activating the displacer (this means that the displacer is moved into the encapsulating material) the connection between the feed means and the mould cavity determined by at least one of the mould parts around an electronic component for encapsulating can in this manner be impeded which makes flow-back of the encapsulating material from the mould cavity to the feed means impossible. In this manner it is also possible to realize that only the encapsulating material in the mould cavity is placed under an increased pressure. There is therefore no need to embody the feed means such that they can also withstand the higher final pressure required in the mould cavity. This for instance has the advantage that the contamination of the feed means becomes better controllable (such as leakage of encapsulating material between a plunger and an associated plunger housing).
The present invention also provides a method for encapsulating electronic components with encapsulating material in a press according to any of the foregoing claims, comprising the processing steps: A) placing an electronic component for encapsulating on a mould part, B) moving the two opposite mould parts toward each other at relatively great speed, C) after processing step B) making the opposite mould parts connect onto each other at a lesser speed such that the electronic component for encapsulating is enclosed, between the mould parts, and D) feeding the encapsulating material to the electronic component, wherein the processing steps B) and C) are forcibly mutually separated in that during processing step C) a safeguard prevents that processing step B) also takes place simultaneously. For the advantages of applying this method reference is made to the advantages as discussed above with reference to the device according to the invention.
In addition, the invention also provides a method for encapsulating electronic components with encapsulating material in a press with displacer, comprising the processing steps: P) placing an electronic component for encapsulating on a mould part, L) moving the two opposite mould parts toward each other such that the electronic component for encapsulating is enclosed between the mould parts, M) feeding liquid encapsulating material to the electronic component under a determined pressure, and N) placing the liquid encapsulating material fed to the electronic component according to the processing step M) under an increased pressure by means of the displacer. By means of this method the advantages can be realized as elucidated above with reference to the press with displacer according to the present invention.